my battery is 81% for a short time can you help me make it 100%

Open Settings ➢ Battery ➢ Battery Health.

If the Maximum Capacity is 80% or less, then it’s time to replace the battery.

iPhone Battery Replacement:

Current Apple Prices:

• No charge for in-warranty or AppleCare+ plan.

Out of Warranty Prices:

• iPhone 14 or newer: $99 U.S. Dollars.
• iPhone X to iPhone 13: $69 U.S. Dollars.
• Older models: $49 U.S. Dollars.

➢ Check AppleCare Coverage.

Click ▶︎ iPhone Battery Replacement.

See if anything here helps

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